RE: N/A v. Turbo heads...(sodium-filled valves)

[Henry Harper <hah@srv.net>]

>> > Are there any differences in the basic cylinder head castings used
>>> on the N/A and turbo I5s?

>> I believe the castings may be the same, but turbos have sodium filled
>> valves, while N/A motors do not.
>
>Ken, you're right, there was a big debate on the list a while ago on how
>to dispose of the sodium filled jobs in a enviromentally responsible
>type of way.  Does anyone know why or what the advantage of sodium
>filled valves is?

I'm a "digest" man so I hope this isn't redundant info...

I found an interesting section in my new Bentley (would you believe I skimmed 
all three volumes the night I got it, read most of the sections that said 
"engine code 3B"?) about disposal of these sodium-filled exhaust valves. It 
says to wear protective attire, grind them apart in the middle (carefully) and, 
stepping back, throw the pieces in a bucket of water (no more than 10 valves 
dumped in at a time, please). After the sodium violently reacts with the water 
in your bucket, the pieces are safe for the trash. Sounds exciting, to say the 
least.

As to why sodium-filled valves: sodium makes an excellent coolant-type fluid at 
slightly elevated temperatures (melts at, what, 200C or so?), one would presume 
to conduct heat away from the valve head/combustion chamber (up the valve stem) 
better than a solid steel valve stem. Valve head too hot => "burned" valve.

Non-Audi trivia: Liquid sodium is used as a coolant in nuclear reactors, one 
that I know is being shut down for political rather than practical reasons here 
in the US (EBR-II, used to work there) and several Japanese and French power 
plants as well as the Russian "Alfa" submarine, which also happens to have a 
titanium pressure hull. Using sodium is a better solution than high-pressure 
water because the sodium can operate at atmospheric pressure with an inert 
cover gas. As for low-pressure water - does a boiling-water reactor sound like 
something you'd like to visit?

Henry Harper
http://www.srv.net/~hah
1991 200 quattro, 79k, euro lights on the way, 10 sodium-filled exhaust valves
1988 GTI 16v, 173k, euro lights since last year, 8 sodium-filled exhaust valves